The subject invention relates to an electro-magnetic actuator having a shortened magnetic flux flow loop.
Many modern vehicles include an engine and an electro-magnetic actuator for controlling a viscous fluid clutch associated with an engine cooling fan. In general operation, the clutch is designed to couple and decouple the fan and the engine. When the clutch is actuated, a rotary force is transmitted from the engine through the clutch to the fan. In this manner, the cooling fan is mechanically driven by the engine. Typically, the rotary force is produced by a water pump pulley within the engine. When the clutch is deactuated, the fan is decoupled from the engine. As such, no rotary force is transmitted from the engine to the fan. The electro-magnetic actuator is used to actuate and deactuate the clutch.
FIG. 1 is a cross-sectional side view of a prior art electro-magnetic actuator 10 attached to a known type of viscous fluid clutch 12. The prior art actuator 10 includes a housing 14, a rotary shaft or core 16, a nut 18, a non-magnetic stainless steel bushing 20, a bearing 22, an electrical coil 24, and a ferromagnetic can 26. The rotary shaft 16, includes a first end portion 28 disposed outside the housing 14 and a second end portion 30 disposed inside the housing 14. The entire shaft 16 is adapted to rotate or spin in relation to the housing 14.
The nut 18 includes an inner peripheral surface 32, an outer peripheral surface 34, and a fastening means 36, such as a thread. The fastening means 36 is adapted to attach the actuator 10 to the clutch 12. When attached, the nut 18 spins with the clutch 12. The stainless steel bushing 20 is adapted to couple the first end portion 28 of the shaft 16 and the inner peripheral surface 32 of the nut 18. When coupled, the shaft 16, the bushing 20,and the nut 18 form a interface surface 38 which spins with the clutch 12.
Conventionally, the actuator 10 is threaded into a mounting and interface port 40 in the clutch 12. In this arrangement, the interface surface 38 is disposed adjacent to a spring-loaded armature plate 42 located inside the clutch 12. The interface surface 38 is spaced from the armature plate 42 to form an air gap 44.
The bearing 22 is disposed around the second end portion 30 of the shaft 16. The bearing 22 is adapted to rotatably support the shaft 16. The electrical coil 24 is disposed around the shaft 16 between the nut 18 and the bearing 22. The electrical coil 24 is adapted to receive electrical current and produce magnetic flux.
The ferromagnetic can 26 is disposed around the shaft 16. The can 26 has a peripheral surface 46 extending between the shaft 16 and the outer peripheral surface 34 of the nut 18. The peripheral surface 46 of the can 26 establishes a path for magnetic flux flow between the shaft 16 and the outer peripheral surface 34 of the nut 18. The peripheral surface 46 of the can 26 is shaped to encase both the electrical coil 24 and the bearing 22 inside the can 26.
The electrical coil 24 forms a ring around the entire shaft 16 inside the can 26. When power is applied to the actuator 10, electrical current flows through the coil 24 producing magnetic flux. The magnetic flux flows in a loop 48, hereinafter referred to as a magnetic flux flow loop, which circles radially about the cross-sectional center point of the coil 24. The magnetic flux consists of magnetic lines of force which collectively constitute a magnetic field. The magnetic field is formed in a toroidal or doughnut like shape around the axis of the shaft 16.
The magnetic flux flow loop 48 is illustrated in FIG. 1. The magnetic flux flow loop 48 extends from the first end portion 28 of the shaft 16 through the length of the shaft 16 to the second end portion 30 of the shaft 16, from the second end portion 30 of the shaft 16 along the peripheral surface 46 of the can 26 around or outside both the bearing 22 and the electrical coil 24 to the outer peripheral surface 34 of the nut 18, from the outer peripheral surface 34 of the nut 18 through the nut 18 to the inner peripheral surface 32 of the nut 18, and between the inner peripheral surface 32 of the nut 18 and the first end portion 28 of the shaft 16 along an arch-shaped airborne path portion 50. The airborne path portion 50 of the magnetic flux flow loop 48 arches outwardly from the actuator 10 around the non-magnetic bushing 20.
When power is applied to the actuator 10, the airborne path portion 50 of the magnetic flux flow loop 48 applies a magnetic force across the air gap 44 onto the armature plate 42 located inside the clutch 12. The magnetic force pulls the armature plate 42 inward, from a spring-loaded closed position to an open position, reducing the air gap 44 between the armature plate 42 and the interface surface 38. In the open position, the armature plate 42 permits fluid flow and coupling within the clutch 12. In this manner, the actuator 10 actuates the clutch 12.
When power is not applied to the actuator 10, the armature plate 42 returns to the spring-loaded off position. In the spring-loaded off position, the armature plate 42 restricts fluid flow and coupling within the clutch 12. In this manner, the clutch 12 is deactuated.
Although the prior art actuator 10 effectively actuates and deactuates the clutch 12, it has several shortcomings. For one, the magnetic flux flow loop 48 about the electrical coil 24 is relatively long, thereby reducing the strength of the clutch actuation force and overall electrical efficiency of the actuator 10. For another, the bearing is a separate component disposed inside the can thus requiring associated labor and assembly time. Accordingly, it would be desirable to provide an electro-magnetic actuator which overcomes the shortcomings of the prior art.
The present invention is an electro-magnetic actuator having a shortened magnetic flux flow loop. The actuator includes a shaft having a first end portion and a second end portion and a nut having an inner peripheral surface and an outer peripheral surface. The inner peripheral surface of the nut is coupled with the first end portion of the shaft. A bearing is disposed around the second end portion of the shaft for rotatably supporting the shaft. An electrical coil is disposed around the shaft between the nut and the bearing for receiving electrical current and producing magnetic flux. A ferromagnetic can is disposed around the shaft having a peripheral surface extending between the shaft and the outer peripheral surface of the nut for establishing a path for magnetic flux flow there between. The peripheral surface of the can is interposed between the electrical coil and the bearing partitioning the electrical coil inside the can and the bearing outside the can. Preferably, the bearing is a circular ball bearing assembly which is insert molded into the actuator.
The present invention provides an electro-magnetic actuator having a shorter magnetic flux flow loop, a stronger clutch actuation force, and a greater electrical efficiency than prior art actuators. Additionally, insert molding the ball bearing assembly into the actuator reduces the cost of the present invention relative to prior art actuators.